1. Field of the Invention
The present invention relates to a joint structure of a cab mounting portion for joining a cab of a forward control vehicle to a chassis frame.
2. Description of the Related Art
As a cab structure of a forward control vehicle, one shown in FIG. 13 is generally adopted. A cab 504 is surrounded by front pillars 509 provided on both right and left sides of a front portion, a front mounting rail 506 provided on an outer surface of the front lower portion, a roof panel 511, a rear panel 512, a side panel 513 and others, and a floor panel 507 is provided on a floor face. Further, cab-under-frames 508 are fixed to the outer surface of the floor panel 507. The cab of the forward control vehicle is coupled to a cab mount bracket which is rotatably provided on a chassis frame in a cab mounting portion.
FIGS. 14 and 15 show an example of the structure of a joint portion for the cab and the chassis frame in the prior art. A cab mount bracket 501 b has a shape allowing contact with a lower surface or a side surface of the cab-under-frame 508 and a rotation center hole 514 for tilt of the cab 504 is formed thereto. Further, as shown in the drawings, the cab-under-frame 508 is fixed to an outer surface of the floor panel 507, and a front end portion of the cab-under-frame 508 is coupled to the front mounting rail 506 side.
In the above-described structure of the joint portion for the cab and the chassis frame, the cab 504 is supported by fastening the cab-under-frame 508 to the cab mount bracket 501b fixed to the chassis frame, and it is configured so as to sufficiently resist vertical external force applied from a road surface side during normal running. However, when a vehicle clashed head-on or bumped from behind, an impact load larger than that obtained during normal running acts in the longitudinal direction. Thus, in the structure of the conventional joint portion for the cab and the chassis frame, since the cab-under-frame 508 and the cab mount bracket 501b are fastened mainly in the vertical direction there is a possibility that the structure can not sufficiently resist the impact load in the longitudinal direction.
On the other hand, as an example of a well-known technique concerning the periphery of the cab mounting member, there are Japanese Utility Model Applications Laid-open Nos. 116277/1981 and 171653/1986. xe2x80x9cThe floor structure of a tilt cabxe2x80x9d in Japanese Utility Model Application Laid-open No. 116277/1981 is a floor constituent member of a tilt cab, in which a front end of a main sill is flange-coupled to a convex shoulder surface of a front cross member constituting the convex shoulder surface on a rear surface side, and a front end of a cab hinge bracket fixed to the main sill is fixed to the convex shoulder surface. In the case of this well-known technique, the rigidity of the coupling portion is insufficient and the coupling rigidity of the cab hinge bracket relative to the main sill is insufficient because the cab hinge bracket is coupled to the convex shoulder surface on the rear surface of the front cross member having the front-open-section. Therefore, the strength against the external force in the longitudinal direction may be possibly insufficient. On the other hand, in xe2x80x9cthe cab structure of an automobilexe2x80x9d disclosed in Japanese Utility Model Application Laid-open No. 171653/1986, a grill bracket is attached to a front surface of a floor frame which supports a outer surface of a floor panel and to which a cab mounting bracket is fixed, and the grill bracket is fixed to the front grill so that the front grill can function as a strength member. However, this structure cannot sufficiently resist the impact load in the longitudinal direction.
In view of the above-described problems, it is an object of the present invention to provide a cab structure that a joint portion for a cab and a chassis frame has the sufficient shear strength and which can disperse external force across the cab or the chassis frame to reduce the burden of load and which can sufficiently resist an impact load in the longitudinal direction.
To achieve this aim, there is provided a cab mounting portion structure in which a xe2x80x9cinside surface portion of a front mounting railxe2x80x9d provided on a cab front lower side is coupled to a xe2x80x9cfront end portion upwardly extending a cab-under-framexe2x80x9d fixed to a floor outer surface, a cab mount bracket is also extended upwardly to be coupled to a vehicle front outer portion of the coupling portion, and these three members are integrally fixed to improve the joint strength.